By use of steady photo-irradiation in the system of riboflavin aqueous solution containing methyl-sulf-amino acid and superoxide dismutase (SOD) as competitive scavenger of O,2, the rate constant of superoxide anion radical (O,2,−,·) scavenged by (Amberacid-chitosan-complex with copper (II), ACCC) was determined as 1.26×10,9, 1.11×10,9, and 4.98×10,8, mol,-1, s,-1, dm,3, under irradiation of 254nm, 365nm UV lights and sun light, respectively. The results also show that the scavenge rate of O,2,−,· by ACCC reached 91%, which is about the same as with natural SOD (93%), and is far more higher than the O,2,−,· scavenge rate with just amberacid or chitosan, which is only 2.6% and 5.8%, respectively.